Three-dimensional periodic structure, method of producing the same, high frequency element, and high frequency apparatus

ABSTRACT

A three-dimensional periodic structure, a method of producing the same, a high frequency element, and a high frequency apparatus that can be applied to a signal transmission path or a functional element in, for example, a compact functional element in a frequency range lower than optical frequencies, such as the microwave range are provided. The three-dimensional periodic structure includes a three-dimensional periodic structure component which includes two substances having different dielectric constants periodically distributed in three-dimensional axial directions, a dielectric layer having a predetermined thickness provided at the periphery thereof, and a conductor provided on external surfaces of the dielectric layer. A third material which is different from the two substances and having predetermined dimensions embedded into the three-dimensional periodic structure component can be provided. A transmission path integrally equipped with a conductor is constructed, which is used as a pipe of a waveguide.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a three-dimensional periodicstructure, a method of producing the same, a high frequency element, anda high frequency apparatus that can be used in electronic parts.

[0003] 2. Description of the Related Art

[0004] A periodic potential distribution in a solid crystal due to thenuclei exhibits interference of an electron wave having a wavelengththat corresponds to the lattice constant. For example, when thewavelength of the electron wave is very close to the potential period ofthe crystal, reflection occurs by three-dimensional diffraction (Braggdiffraction). This phenomenon prevents the passage of electrons in aspecific energy range. Thus, an electronic band gap, which is utilizedin semiconductor devices, is formed.

[0005] Similarly, a three-dimensional structure having a periodicallychanging refractive index or dielectric constant exhibits interferenceof electromagnetic waves, thus blocking the electromagnetic waves in aspecific frequency range. In this case, the forbidden band is called aphotonic band gap and the three-dimensional structure is called aphotonic crystal.

[0006] The effect of such a photonic crystal has been considered for useto provide a cut-off filter that prevents penetration of electromagneticwaves within a predetermined frequency band, or to provide a waveguideor a resonator by introducing a nonuniform part that disturbs thefrequency to trap light or electromagnetic waves into the periodicstructure. Applications such as ultra-low threshold lasers orelectromagnetic highly directional antennas are also considered.

[0007] In general, in a photonic crystal, two types of standing wavesare formed when the electromagnetic waves produce Bragg diffraction.FIG. 1 shows the two types of standing waves. Standing wave A has highenergy at a low dielectric constant area of the wave vibration whilestanding wave B has high energy at a high dielectric constant area ofthe wave vibration. Waves having energy between the standing waves thatsplit into two different modes cannot exist in the crystal, therebyproducing the band gap. In order to broaden the band gap, the energydifference between the two standing waves is increased. This can beachieved by strengthening the contrast between the dielectric constantsof two media to a high degree, or increasing the volume ratio of themedia having the high dielectric constant.

[0008] The photonic crystal has a one-, two-, or three-dimensionalstructure. A three-dimensional structure is needed for a photonic bandgap. In order to provide a three-dimensional structure, JapaneseUnexamined Patent Application Publication No. 10-335758 discloses “Athree-dimensional periodic structure, a method of producing the same,and method of producing a film”, Japanese Unexamined Patent ApplicationPublication No. 2000-329953 discloses “A photonic crystal and a methodof producing the same”, Japanese Unexamined Patent ApplicationPublication No. 2000-341031 discloses “A three-dimensional periodicstructure and a method of producing the same”, Japanese UnexaminedPatent Application Publication No. 2001-74954 discloses “Athree-dimensional photonic crystal structure and a method of producingthe same”, Japanese Unexamined Patent Application Publication No.2001-215351 discloses “A periodic structure element having multipledielectric constants, a method of designing the same, and a method ofproducing the same”, Japanese Unexamined Patent Application PublicationNo. 20001-58542 discloses “A structure, a multilayer structure, a methodof producing the same, and an apparatus therefor”, and JapaneseUnexamined Patent Application Publication No. 2000-258645 discloses “Athree-dimensional periodic structure, a two dimensional structure, and amethod of producing them”.

[0009] These three-dimensional periodic structures have been inventedfor application to various devices utilizing its photonic band gap.However, they do not suggest an electrode arrangement of thethree-dimensional periodic structure. Also, they do not suggestapplications for a waveguide in the microwave or millimeter wave range.When these three-dimensional periodic structures are used to construct atransmission path, the path becomes undesirably large.

SUMMARY OF THE INVENTION

[0010] An object of the present invention is to provide athree-dimensional periodic structure, a method of producing the same, ahigh frequency element, and a high frequency apparatus that can beapplied to a compact signal transmission path or a functional elementin, for example, the microwave range.

[0011] In one aspect, a three-dimensional periodic structure of thepresent invention comprises two substances having different dielectricconstants periodically distributed in three-dimensional axial directionsin three-dimensional space, a coated layer having a predeterminedthickness and made of one of the two substances, the coated layers beingprovided at the periphery of the three-dimensional space, and aconductive film provided on an external surface of the coated layer. Atthe periphery of the three-dimensional space, conductors can beintegrated to significantly decrease required numbers of parts, and makethe structure compact.

[0012] Space having predetermined dimensions and constituted by one ofthe two substances is provided in the three-dimensional space of theperiodic structure. Such a three-dimensional periodic structure caneasily be periodically broken locally. By suitably selecting the shape,size and position of the space, spurious-mode frequencies, blockingfrequency bands, the bandwidth, the attenuation and the like can beadjusted.

[0013] According to the present invention, a resonator comprises thethree-dimensional periodic structure of the present invention and acoupling part which is coupled to an electromagnetic field in aresonance mode in the space surrounded by the conductive film of thethree-dimensional periodic structure. A compact and lightweightresonator or filter can thus be easily provided.

[0014] According to the present invention, a transmission path comprisesthe three-dimensional periodic structure of the present invention and acoupling part which is coupled to an electromagnetic field in atransmission mode in the space surrounded by the conductive film of thethree-dimensional periodic structure. The transmission path having afilter function can thereby be provided.

[0015] According to the present invention, an antenna comprises thethree-dimensional periodic structure of the present invention and awindow through which electromagnetic waves penetrate provided on theconductive film of the three-dimensional periodic structure. The antennahaving a filter function can thus be provided.

[0016] In the antenna, the three-dimensional periodic structure hasdifferent crystal periods in predetermined three-dimensional directions,and the windows are provided thereon in the predeterminedthree-dimensional directions with the different crystal periods. Asingle antenna having various radiation characteristic can thereby beprovided without any special element.

[0017] According to the present invention, a branching filter comprisesthe antenna of the present invention and a transmission path provided atthe window of the antenna. The branching filter can be made compact.

[0018] According to the present invention, an isolator comprises asignal transmission path including the transmission path of the presentinvention. An isolator having a filter function is thereby provided.

[0019] According to the present invention, a coupler comprises a signaltransmission path including the transmission path of the presentinvention. The coupler having a filter function can thus be provided.

[0020] According to the present invention, a high frequency apparatuscomprises any one of the resonator, the transmission path, the antenna,the branching filter, the isolator and the coupler as described above.

[0021] In another aspect, a method of producing a three-dimensionalperiodic structure by stereolithography method of the present inventioncomprises repeating the step of irradiating light onto alight-hardenable resin in each layer cross-sectional pattern to beformed to form the three-dimensional periodic structure of the presentinvention where either of the two substances is distributed, and formingthe conductive film of the present invention by electroless plating. Athree-dimensional periodic structure having conductors integrally at theperiphery can be easily produced.

[0022] In another aspect, a three-dimensional periodic structure of thepresent invention comprises two substances having different dielectricconstants periodically distributed in three-dimensional axialdirections, the two substances occupying a three-dimensional space withpredetermined external dimensions, and a material having predetermineddimensions and comprising a different substance from the two substancesembedded into the three-dimensional space. When such three-dimensionalperiodic structure is applied to a frequency range lower than opticalfrequencies, such as the microwave range, the three-dimensional periodicstructure does not become large-sized in contrast to where twosubstances having different dielectric constants are simply periodicallydistributed in a three-dimensional axial direction. Thus, thethree-dimensional periodic structure of the present invention can beapplied to a functional element in a frequency range lower than opticalfrequencies.

[0023] In the three-dimensional periodic structure of the presentinvention, one of the two substances can be air arranged as holes in adiamond crystal lattice structure, and wherein the material comprisingthe substance different from the two substances is provided in aplurality of the air holes. The material can be easily positioned.

[0024] In yet another aspect, a three-dimensional periodic structure ofthe present invention comprises two substances having differentdielectric constants simply periodically distributed inthree-dimensional axial directions, the two substances occupying athree-dimensional space with predetermined external dimensions, and aspace having predetermined dimensions in which one of the two substancesis filled, provided in the three-dimensional space. When suchthree-dimensional periodic structure is applied to a frequency rangelower than optical frequencies, such as the microwave range, thethree-dimensional periodic structure does not become large-sized incontrast to where two substances having different dielectric constantsperiodically distributed in a three-dimensional axial direction. Thus,the three-dimensional periodic structure of the present invention can beapplied to a functional element in a frequency range lower than opticalfrequencies.

[0025] In the three-dimensional periodic structure of the presentinvention, the three-dimensional periodic structure has changed periodsalong predetermined three-dimensional axial directions. The number ofdesigning parameters is increased as compared with the case where theperiod is constant, resulting in a highly functional three-dimensionalperiodic structure.

[0026] According to the present invention, a transmission pathcomprising the three-dimensional periodic structure provided within awaveguide is provided. The transmission path can provide a filter actionto signals, for example, within the microwave range.

[0027] According to the present invention, a transmission pathcomprising the three-dimensional periodic structure provided on onesurface or both surfaces of a substrate which constitutes a part of thetransmission path is provided. The transmission path can provide afilter action to signals, for example, within the microwave range.

[0028] In the transmission path, the substrate comprises a transmissionline made of a conductive film. The transmission path can have bothcharacteristics as the transmission path comprising the conductive filmand the substrate, and electrical characteristics provided by thethree-dimensional periodic structure.

[0029] In the transmission path, the substrate can have a multilayerstructure comprising circuit elements, including a capacitor, aninductor, and an interlayer connection. The transmission path can bemultifunctional having the electrical characteristics of the circuits onthe substrate.

[0030] According to the present invention, a filter comprising thetransmission path for utilizing the transmission characteristics thereofis provided. The filter can have the transmission characteristics of thetransmission path.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 is a diagram showing two standing waves when substanceshaving different dielectric constants are periodically distributed.

[0032]FIGS. 2A and 2B are a perspective view and a sectional view of atransmission path according to a first embodiment of the presentinvention.

[0033]FIG. 3A is a diagram showing the structure of a stereo lithographyapparatus.

[0034]FIGS. 3B is a sectional view showing a light-hardening resinirradiated with a laser beam.

[0035] FIGS. 4 to 4C are diagrams each showing an object being formed bya stereo lithography apparatus.

[0036]FIGS. 5A to 5D show process steps of producing a three-dimensionalperiodic structure by stereo lithography.

[0037]FIG. 6 is a sectional view of a transmission path according to asecond embodiment of the present invention.

[0038]FIGS. 7A and 7B are sectional views of another transmission pathaccording to a second embodiment of the present invention.

[0039]FIGS. 8A and 8B are a perspective view and a sectional view of afilter according to a third embodiment of the present invention.

[0040]FIG. 9 is a graph showing characteristics of the filter.

[0041]FIGS. 10A to 10C are a perspective view and sectional views eachshowing a filter according to a fourth embodiment of the presentinvention.

[0042]FIG. 11 is a perspective view of a transmission path according toa fifth embodiment of the present invention.

[0043]FIG. 12 is a sectional view of an antenna according to a sixthembodiment of the present invention.

[0044]FIG. 13 is a block diagram of a branching filter according to aseventh embodiment of the present invention.

[0045]FIG. 14 shows the construction of an isolator according to aneighth embodiment of the present invention.

[0046]FIG. 15 shows the construction of a coupler according to a ninthembodiment of the present invention.

[0047]FIG. 16 shows the construction of a radar according to a tenthembodiment of the present invention.

[0048] different FIG. 17 is a perspective view of a transmission pathaccording to an eleventh embodiment of the present invention.

[0049]FIG. 18 is a sectional view of the transmission path.

[0050]FIGS. 19A to 6D show stages in the process for producing athree-dimensional periodic structure by stereolithography.

[0051]FIG. 20 is a sectional view of a transmission path according to atwelfth embodiment of the present invention.

[0052]FIG. 21 is a sectional view of a transmission path according to athirtenth embodiment of the present invention.

[0053]FIG. 22 is a graph showing penetration characteristics of thetransmission path.

[0054]FIGS. 23A and 23B are sectional views each showing a transmissionpath according to a fourteenth embodiment of the present invention.

[0055]FIG. 24 is a perspective view of a transmission path according toa fifteenth embodiment of the present invention.

[0056]FIG. 25 is a perspective view of a substrate used for thetransmission path.

[0057]FIG. 26 is an exploded perspective view showing anotherconstruction of a substrate.

[0058]FIG. 27 is a perspective view of a slot antenna using theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0059] Referring to FIGS. 2 to 5, a transmission path according to afirst embodiment of the present invention will be described.

[0060]FIG. 2A is a perspective view of the transmission path. FIG. 2B isa sectional view orthogonal to the signal transmission direction.

[0061] A three-dimensional periodic structure component 100 in which adielectric layer 1′ and air holes are periodically distributed in thethree-dimensional axes is shown. The dielectric layer 1′ having apredetermined thickness is provided around the three-dimensionalperiodic structure component 100. The dielectric layer 1′ includes noair holes, and an external conductor 8 is formed on the surface of thedielectric layer 1′ so that the external conductor 8 covers the surfacesof the dielectric layer 1′ extending in the longitudinal direction. Thethree-dimensional periodic structure 101 is constituted by thethree-dimensional periodic structure component 100, the dielectric layer1′, and the external conductor 8.

[0062] The three-dimensional periodic structure component 100 acts as aphotonic crystal. In order for the photonic crystal to develop asufficient electromagnetic-wave reflectivity, it is necessary to form awide band gap in all crystal directions. An ideal crystal structure is athree-dimensional diamond structure. In the diamond structure, a unitlattice includes eight lattice points; four of which form an independentface centered cubic lattice, and one lattice is located at a position sothat the lattice is moved ¼ of the length of the other lattice along asteric diagonal line.

[0063] A diamond-structure photonic crystal is a crystal in whichspherical dielectrics are located at the lattice points of the diamondstructure, that is, a crystal that simulates atomic bonds of the diamondstructure by combining dielectric columns.

[0064] In the three-dimensional periodic structure component 100 shownin FIGS. 2A and 2B, air holes in the diamond-type lattice structure areperiodically distributed in a resin. Such a structure can be referred toas a reverse diamond structure. The ratio of the diameter to the lengthin columns in the lattice shown is 2:3 (aspect ratio 1.5). The latticeconstant is 10 mm.

[0065] The three-dimensional periodic structure component 100 thusconstructed attenuates a predetermined frequency band by its photonicband gap. The three-dimensional periodic structure component 100 isconstructed in advance so that the frequency band to be blocked ismatched with the frequency band attenuated by the photonic band gap,whereby the three-dimensional periodic structure 101 acts as atransmitting path that transmits only the frequency band desired to betransmitted, and blocks unwanted frequency components.

[0066]FIG. 3A shows a stereolithography apparatus for producing a mainpart of the three-dimensional periodic structure 101 shown in FIG. 2A. Acontainer 15 filled with an epoxy-based light-hardenable resin 18 thatcan be hardened by ultraviolet rays, an elevator table 16 that movesupward and downward within the container 15, an object 19 formed on thetop of the elevator table 16, and a squeegee 17 for coating thelight-hardenable resin 18 on the top surface of the object 19 to apredetermined film thickness are shown.

[0067] Also, a laser diode 10, a harmonic generating element (LBO) 11for changing the wavelength of the laser light from the laser diode 10to produce ultraviolet rays, an acousto-optical element (AOM) 12functioning as a wavelength selecting element, a scanning mirror 13, andfθ lens 14 are shown. Thus, an optical system is configured.

[0068] A process sequence for producing the photonic crystal using thestereolithography apparatus is described below.

[0069] First, the elevator table 16 is lowered from the liquid surfaceof the light-hardening resin 18 to a predetermined depth. The squeegee17 is moved along the liquid surface to form a light-hardenable resinfilm having a thickness of about 150 μm on the surface of the elevatortable 16. The liquid surface is then irradiated with ultraviolet rayshaving a wavelength of 355 nm with a spot diameter of 50 μm and anoutput power of 110 mW by the optical system. The scanning mirror 13 iscontrolled to modulate the laser diode 10 so that the laser light isirradiated to an area where the light-hardening resin 18 is to behardened, but is not irradiated to other areas.

[0070] A spherical hardened phase having a diameter of 100 μm is formedby a polymerization reaction on the liquid surface of thelight-hardenable resin 18 irradiated with the laser beam. When the laserbeam is scanned at a speed of 90 m/s, a hardened phase having athickness of 150 μm is formed. The object 19 is formed corresponding toa first layer cross-sectional pattern by raster scanning the laser beam.

[0071] Then, the elevator table 16 is lowered by about 200 μm. Thesqueegee 17 is moved to form a light-hardenable resin film having athickness of about 200 μm on the surface of the object 19.

[0072] Thereafter, a second layer cross-sectional pattern is formed onthe first layer by scanning and modulating the laser beam similarly tothe first layer. The first and second layers adhere by polymerizationhardening. Third and subsequent layers are formed in the same manner. Byrepeating this processing, the object 19 is constructed.

[0073]FIGS. 4A to 4C are perspective diagrams each showing an object ineach of the steps for forming a number of layers. For simplicity, partsthat are not hardened with laser beam irradiation, i.e., the holepatterns, are shown. FIG. 4A shows substantially only one unit in the<111> crystal axis direction of the diamond structure. FIG. 4B showssubstantially four units. FIG. 4C shows several units.

[0074] In the apparatus shown in FIG. 3A, a CAD/CAM process is used toharden the light-hardenable resin 18 in the predeterminedcross-sectional patterns at the liquid surface of the light-hardenableresin 18. Specifically, the patterns shown in FIGS. 4A to 4C aredesigned in advance by a CAD system capable of handlingthree-dimensional data. The three-dimensional data is converted into STL(stereolithography) data. The STL data is converted into sets oftwo-dimensional data at predetermined positions using slicing software.Finally, data for modulating the laser diode when the laser beam israster scanned is created with the two-dimensional data. Based on thethus-prepared data, the laser beam is scanned, and the laser diode ismodulated.

[0075]FIGS. 5A to 5D show process steps of producing a three-dimensionalperiodic structure 101 by the aforementioned stereolithographyapparatus. As shown in FIG. 5A, the dielectric layer 1′ is produced bystereolithography so that it has a predetermined thickness. Then, thestereolithography is further patterned so that the three-dimensionalperiodic structure component 100 is formed within the dielectric layer1′ having the predetermined thickness. Thereafter, the surface of thedielectric layer 1′ is coated with the external conductor 8 byelectroless plating, thereby providing the three-dimensional periodicstructure 101 as shown in FIGS. 2A and 2B.

[0076] Now, referring to FIG. 6 and FIGS. 7A and 7B, a transmission pathaccording to a second embodiment of the present invention will bedescribed.

[0077]FIG. 6 is a sectional view orthogonal to a signal transmissiondirection. A dielectric 1 and air holes 2 are shown. The dielectric 1and the air holes 2 periodically distributed in the three-dimensionalaxial directions together constitute a three-dimensional periodicstructure component 100. Voids 7 extending in the signal transmissiondirection are formed at predetermined positions, which are differentfrom those shown in FIGS. 2A and 2B. A dielectric layer 1′ with apredetermined thickness having no air holes is formed around thethree-dimensional periodic structure component 100, and an externalconductor 8 is formed around layer 1′.

[0078] By providing the voids 7 within the three-dimensional periodicstructure 101, the effect of the crystal structure of thethree-dimensional periodic structure 101 on electromagnetic waves to betransmitted changes. By suitably selecting the shape, the size and theposition of each void 7, spurious-mode frequencies can be adjusted.Also, the blocking frequency band, the bandwidth, the attenuation andthe like can be adjusted to some degree.

[0079]FIGS. 7A and 7B each show another transmission path having adifferent structure from that shown in FIG. 6. FIG. 7A is a longitudinalcross-section taken along the signal transmission direction. FIG. 7B isa longitudinal cross-section taken in a plane orthogonal to the signaltransmission direction. A probe 20 and a central conductor 20′ thereofare shown. In this example, a void 7 extending in the vertical directionor the signal transmission direction is formed at a center of thethree-dimensional periodic structure component 100 as shown in FIG. 7B.The central conductor 20′ of the probe is inserted into void 7. The void7 acts as a cavity waveguide. The surrounding three-dimensionalstructure component 100 blocks predetermined unwanted frequencies.Therefore, signals in the frequency band to be transmitted areconcentrated in the void 7. Thus, the void 7 acts as the cavitywaveguide.

[0080] In the embodiments shown in FIGS. 67A and 7B, thethree-dimensional space is filled with the void(s) of a predeterminedsize. Similarly, the three-dimensional space may be filled with adielectric in a predetermined size.

[0081] With such a structure, a transmission path having a filterfunction with decreased loss can be provided.

[0082] Referring to FIGS. 8A and 8B, a filter according to a thirdembodiment of the present invention will be described.

[0083]FIGS. 8A and 8B are a perspective view and a sectional view of thefilter. An external conductor 8 of the three-dimensional periodicstructure is shown. Two openings are covered by panels 22 a and 22 b.Connection loops 24 a and 24 b that are connected to coaxial connectors23 a and 23 b and a center conductor are formed on the panels 22 a and22 b. The three-dimensional periodic structure 101 may be any structureshown in the first or second embodiment except that spaces for insertingthe connection loops 24 a and 24 b are formed in advance at end faces ofthe three-dimensional periodic structure 101.

[0084] Basically, the three-dimensional periodic structure 101 functionsas a cavity resonator or a cavity waveguide. Since the three-dimensionalperiodic structure component 100 exists, frequencies corresponding tothe photonic band gap are attenuated. By tuning a resonance frequency ina spurious mode with the frequency attenuated, the filter functions as aband rejection filter that rejects the frequency band of the attenuatedfrequency.

[0085]FIG. 9 shows penetration characteristics of the filter. In thisembodiment, the filter functions as a band rejection filter forattenuating a frequency band of 11 GHz.

[0086] Referring to FIGS. 10A to 10C, a filter according to a fourthembodiment of the present invention will be described.

[0087]FIG. 10A is a perspective view of the filter. FIG. 10B is asectional view showing a main part thereof. FIG. 10C is a sectional viewshowing another filter. A three-dimensional periodic structure component100 is shown. On an external surface of the structure, a dielectriclayer 1′ and protrusions 26 are formed. The protrusions 26 are formed ofa dielectric which is continuous with the dielectric layer 1′. Anexternal conductor 8 is formed on external surfaces of the dielectriclayer 1′. Windows 27 having no external conductor 8 are formed at thebottom of the protrusions 26. Electrodes 28 are formed on the surfacesof the protrusions 26. The electrodes 28 are insulated from the externalconductor 8 by the windows 27.

[0088] In such a structure, the external conductor 8 disposed around thethree-dimensional periodic structure 101 acts as a cavity of a cavityresonator, the windows 27 act as windows for external connection, andthe electrodes 28 on the surfaces of the protrusions 26 act as probes.Thus, a filter integrally having external input and output parts(probes) can be formed by forming a conductor (electrode) film on thethree-dimensional periodic structure formed by stereolithography.

[0089] In FIG. 10C, the windows 27 are recessed, and the bottom of theprotrusions 26 is lower than the top surface of the external conductor8. Accordingly, the electrodes 28 around the protrusions 26 are partlyinserted into resonant space. With such a structure, the electrodes 28functioning as the probes can be strongly connected to the resonator.

[0090] Referring to FIG. 11, an antenna according to a fifth embodimentof the present invention will be described.

[0091]FIG. 11 is a perspective view of an antenna. A three-dimensionalperiodic structure component 100 is shown. A dielectric layer 1′ havinga predetermined thickness is formed around component 100. An externalconductor 8 is formed on four sides of the dielectric layer 1′. Aplurality of windows 27 are arranged and formed in part of the externalconductor 8. The external conductor 8 acts as a waveguide. The windows27 act as windows for electromagnetic waves. The electromagnetic wavestransmitted through the waveguide are radiated from the windows 27.

[0092] By utilizing attenuation characteristics of a predeterminedfrequency of the three-dimensional periodic structure 101, thetransmission or reception of unwanted frequency components can beprevented.

[0093] The windows 27 may have a slot-like shape to construct aso-called slot antenna.

[0094] Referring to FIG. 12, an antenna according to a sixth embodimentof the present invention will be described.

[0095]FIG. 12 is a sectional view orthogonal to the signal transmissiondirection. A three-dimensional periodic structure component 100 isshown. A dielectric layer 1′ having a predetermined thickness is formedaround component 100. An external conductor 8 is formed on a surface ofthe dielectric layer 1′. The three-dimensional periodic structurecomponent 100 is configured so that the crystal period is graduallychanged in a predetermined direction (the vertical direction in FIG.12), unlike the antenna shown in FIG. 11. Windows ha, hb, hc, and hd aredisposed on the external conductor 8. The four sides thereof have thewindows ha to hd, unlike the antenna shown in FIG. 11.

[0096] Thus, the crystal period of the three-dimensional periodicstructure component 100 is gradually changed along a predetermined axisdirection, whereby directivity can be changed corresponding to thefrequency. The windows are disposed on plural sides, whereby the signalsin different frequency bands can be radiated in a predetermineddirection.

[0097] The three-dimensional periodic structure component 100 has acrystal period that gradually changes along the predetermined axialdirection. Accordingly, the photonic band gap differs depending on thetransmission direction of electromagnetic waves. As a result, there isprovided different directivity depending on the frequency.

[0098] Referring to FIG. 13, a branching filter according to a seventhembodiment of the present invention will be described.

[0099] In the embodiment shown in FIG. 12, the electromagnetic waves areradiated from the windows ha to hd disposed on the external conductor 8.Frequency characteristics of the radiant efficiency in each window aredetermined by the crystal period of the three-dimensional periodicstructure component 100 and the position of each window. In other words,the electromagnetic waves can be selectively radiated from each windowdepending on their frequency. Accordingly, a transmission path fortransmitting the electromagnetic waves radiated from the windows shownin FIG. 12 is provided, which can be used as a branching filter. FIG. 13shows a block diagram thereof. In this embodiment, the windows aredisposed at three sides of the three-dimensional periodic structure. Theelectromagnetic waves are inputted to one of the windows, and outputtedfrom the remaining two windows.

[0100] Referring to FIG. 14, an isolator according to an eighthembodiment of the present invention will be described.

[0101]FIG. 14 is a sectional view orthogonal to the signal transmissiondirection. In the isolator, a dielectric layer 1′ having a predeterminedthickness is shown disposed around the periphery of a three-dimensionalperiodic structure component 100. An external conductor 8 is coated andformed around component 100. The thus-constructed three-dimensionalperiodic structure acts as a rectangular waveguide. A ferrite plate 25is inserted into the rectangular waveguide at an asymmetric positionwith respect to the center of the external conductor 8. A direct currentmagnetic field Hdc is applied from outside the ferrite plate 25. In theTE10 mode in rectangular waveguide, there exists vibration magneticfields Hx and Hz that differ in phase by 90°, and the combined rotatingmagnetic field is elliptically polarized in the y-z plane at optionalone point. The rotation direction of the polarized wave is opposite onboth sides of the y-z plane including the tube axis. A wave propagatingin the positive z direction is also opposite to a wave propagating inthe negative z direction. By appropriately selecting the direct currentmagnetic field Hdc, the wave propagating in the positive z directionproduces a positive rotating magnetic field and is attenuated byresonance absorption. The wave propagating in the negative z directionis not attenuated. Thus, the structure functions as an isolator. In thiscase, the three-dimensional periodic structure component 100 isprovided, whereby unwanted frequency bands transmitted through thewaveguide are attenuated. The isolator can be used as an isolator havinga filter function.

[0102] The three-dimensional periodic structure component 100sandwiching the ferrite 25 can be produced separately. Alternatively,the ferrite 25 may be embedded into a single three-dimensional periodicstructure component 100, and they may be integrated to form athree-dimensional periodic structure.

[0103] Referring to FIG. 15, a coupler according to a ninth embodimentof the present invention will be described.

[0104] In the coupler, two transmission paths are aligned, andconnection elements for connecting waves in both transmission paths areprovided on walls of the transmission paths. In this embodiment, holesha and hb are provided as the connecting waves, separated by ¼ of thewavelength in the waveguide. Signals transmitted from a port #1 to aport #2 are added in-phase at port #4 and outputted, but are added innegative-phase at port #3, so that they cancel and are not outputted.

[0105] The two transmission paths may be any structure shown in thefirst or second embodiment. The coupler transmits the frequency bands tobe transmitted, and acts as a filter for blocking unwanted frequencybands.

[0106] Referring to FIG. 16, a radar according to a tenth embodiment ofthe present invention will be described.

[0107] In FIG. 16, an oscillator 31, an amplifier 32 for amplifyingoscillated signals, an isolator 33 for preventing the signals fromreturning to the amplifier 32, and a coupler 34 for taking out a part ofthe signals transmitted as local signals are shown. Also, an antenna 36,a mixer 37, and a circulator 35, which outputs the signals transmittedto the antenna 36 and outputs the signals received from the antenna 36to the mixer 37, are shown. The mixer 37 mixes the received signals withthe local signals to produce beat signals. A filter 38 takes necessaryfrequency components of the beat signals, and outputs them as receivedintermediate frequency (IF) signals.

[0108] The isolator 33 is shown in FIG. 14. The coupler 34 is shown inFIG. 15. The antenna 36 is shown in FIG. 11 or 12. The individualtransmission paths are shown in FIGS. 2, 6 and 7. Thus, a compact andhigh sensitivity radar having low spurious characteristics isconstructed by using the high frequency element with a filteringfunction.

[0109] Referring to FIGS. 17 to 19, a three-dimensional periodicstructure, a method of producing the same, and a transmission pathaccording to an eleventh embodiment of the present invention will bedescribed.

[0110]FIG. 17 is a perspective view showing a transmission path. FIG. 18is a sectional view thereof. A waveguide 4 is shown. A three-dimensionalperiodic structure 101 is provided within the waveguide 4. In FIG. 17, adielectric 1, which is formed of one substance of a three-dimensionalperiodic structure component 100, and air holes 2, which is the othersubstance, are shown. The dielectric 1 and the air holes 2 togetherconstitute the three-dimensional structure component 100. A rectangulardielectric 3 extends along the signal transmission direction of thewaveguide 4. The three-dimensional periodic structure component 100 andthe rectangular dielectric 3 together constitute the three-dimensionalperiodic structure 101.

[0111] The three-dimensional periodic structure component 100 acts as aphotonic crystal. In order for the photonic crystal to develop asufficient electromagnetic-wave reflectivity, it is necessary to form awide band gap in all crystal directions. An ideal crystal structure is athree-dimensional diamond structure. In the diamond structure, the unitlattice includes eight lattice points; four of which make an independentface centered cubic lattice, and one lattice is located at a position sothat the lattice is moved ¼ of the length of the other lattice along asteric diagonal line.

[0112] The eleventh embodiment can be produced as described inconnection with FIGS. 3 to 5. FIGS. 19A to 19D show stages of theproduction of a three-dimensional periodic structure by theaforementioned stereolithography apparatus. As shown in FIG. 19A, athree-dimensional periodic structure component 100 is formed bystereolithography so that it has a predetermined thickness. Then, thethree-dimensional periodic structure component 100 is further formed bystereolithography to provide a groove d as shown in FIG. 19B. Apre-formed rectangular dielectric 3 is inserted into the groove as shownin FIG. 19C. The three-dimensional periodic structure component 100 isthen formed over the dielectric 3, thereby providing a three-dimensionalperiodic structure 101 where the dielectric 3 is embedded into thethree-dimensional periodic structure component 100, as shown in FIG.19D.

[0113] The three-dimensional periodic structure 101 thus formed isdisposed within the waveguide 4. This waveguide 4 can provide atransmission path showing penetration characteristics such that apredetermined frequency is significantly attenuated by the photonic bandgap of the three-dimensional periodic structure component 100.

[0114] In addition, the electromagnetic field in a predeterminedtransmission mode is converged on the rectangular dielectric 3 at thecenter of the waveguide 4, and the whole transmission path acts as adielectric line.

[0115] The transmission of the dielectric line can be made to correspondwith a signal frequency band to be transmitted, while at the same time,a frequency range attenuated by the three-dimensional periodic structurecomponent 100 is made to correspond with a frequency band to be blocked.As a result, a transmission path having a filter function that transmitsonly signal components of the frequency band to be transmitted can beprovided.

[0116] Referring to FIG. 20, a transmission path according to a twelfthembodiment of the present invention will be described.

[0117]FIG. 20 is a sectional view of the transmission path. A dielectric1 and air holes 2 are shown. The dielectric 1 and the air holes 2together constitute a three-dimensional periodic structure. Dielectricpieces 3′ are embedded into predetermined air holes 2. Athree-dimensional periodic structure 101 including the dielectric 1, theair holes 2, and the dielectric pieces 3′ is disposed within thewaveguide 4.

[0118] The three-dimensional periodic structure 101 is produced byrepeating the step of forming the dielectric 1 and the air holes 2 bystereolithography, and the step of placing the dielectric pieces 3′,each having a size that fits the air holes, into the air holes using thestereolithography apparatus shown in FIG. 3A.

[0119] By distributing the dielectric pieces 3′, which are made of adifferent material from that of the dielectric 1, in the lattice of thethree-dimensional periodic structure, the three-dimensional periodicstructure 101 can have transmission and blocking characteristics indifferent frequency bands depending on the distribution of thedielectric pieces 3′.

[0120] A conductor film may be formed on the surfaces of the dielectricpieces 3′. Alternatively, any conductive material, such as metal, may bedistributed instead of the dielectric material, whereby the penetrationcharacteristics of the transmission path can be determined depending ontheir distribution.

[0121] Referring to FIGS. 21 and 22, a transmission path according to athirteenth embodiment of the present invention will be described. FIG.21 is a sectional view of the transmission path. A substrate 5 and athree-dimensional periodic structure component 100 are disposed so thatthe substrate is sandwiched in the component as shown. The substrate 5has a higher dielectric constant than the two substances in thethree-dimensional periodic structure component 100. Thethree-dimensional periodic structure comprising the substrate 5 and thethree-dimensional periodic structure component 100 are disposed within awaveguide 4.

[0122] In FIG. 21, the three-dimensional periodic structure component100 has the same structures as those of the three-dimensional periodicstructure components 100 in the first and second embodiments. Thesubstrate 5 is a dielectric ceramic substrate or a resin substrate. Thethree-dimensional periodic structures 100 are independently disposed tosandwich the substrate 5. Alternatively, the substrate 5 may be embeddedinto a single three-dimensional periodic structure component.

[0123]FIG. 22 shows penetration characteristics of the transmission pathwith and without the substrate 5. By disposing a substrate 5 having ahigher effective dielectric constant than that of the three-dimensionalperiodic structure component 100, the blocking frequency band is shiftedto lower frequencies, and the attenuation is increased. This is becausethe substrate has the higher effective dielectric constant, and theblocking conditions change according to the shape and size of thesubstrate.

[0124] Referring to FIGS. 23A and 23B, a transmission path according toa fourteenth embodiment of the present invention will be described.

[0125]FIGS. 23A and 23B are sectional views each showing a transmissionpath. Three-dimensional periodic structures each comprise a substrate 5and three-dimensional periodic structure components 100 a and 100 b aredisposed within a waveguide 4 similar to that shown in FIG. 21.

[0126] In FIG. 23A, a void 7 extending in the signal transmissiondirection is disposed in the three-dimensional periodic structurecomponent 100 a. In FIG. 23B, the three-dimensional structure components100 a and 100 b have different three-dimensional periods inpredetermined axial directions. Thus, the waveguide can have differentblocking characteristics in frequency bands at different sites of thewaveguide. The electrical characteristics of the whole waveguide can bedetermined freely, as compared with the case where a uniformthree-dimensional periodic structure is present.

[0127] The three-dimensional periodic structure components 100 a and 100b may have a periodic shifting structure where the frequency issequentially changed along a predetermined axis.

[0128] Referring to FIGS. 24 to 26, a transmission path according to afifteenth embodiment of the present invention will be described.

[0129]FIG. 24 is a perspective view of a transmission path having apredetermined length in the signal transmission direction; thetransmission path is cut at a surface orthogonal to the signaltransmission direction. In FIG. 24, a substrate 5 constituting a mainpart of the transmission path is shown. Three-dimensional periodicstructures 101 are disposed above and below the main part of thesubstrate 5. That is, the three-dimensional periodic structures 101sandwich the substrate 5.

[0130]FIG. 25 is a perspective view where the three-dimensional periodicstructures 101 are removed from the configuration shown in FIG. 20.Above and below of the substrate 5, electrodes 6 extending in the signaltransmission direction are formed. The substrate 5 and the electrodes 6formed thereon constitute various transmission lines, such as striplines, slot lines and coplanar lines. Alternatively, a block may bedisposed around the substrate to constitute a suspended line.

[0131]FIG. 26 is an exploded perspective view showing anotherconstruction of a substrate. While the transmission line is constitutedby forming the electrodes 6 on a single dielectric substrate in FIG. 25,a multilayer substrate including five layers 5 a to 5 e is shown in FIG.26. Layer 5 a includes a coil-patterned electrode, layer 5 b includes acapacitor-patterned electrode, layer 5 c includes a block pattern andlayer 5 d includes a trimmer electrode. An interlayer connectionconductor is formed at a cross-section of or inside the substrate usingthe so-called LTCC technology. Thus, a multilayer substrate including acircuit element such as a capacitor, an inductor and the interlayerconnection conductor may be used, whereby the electrical characteristicsof the substrate and the blocking characteristics of thethree-dimensional periodic structure 101 can be provided simultaneously.

[0132]FIG. 27 is a perspective view of a slot antenna. The antennacomprises a waveguide 4 and the three-dimensional periodic structure 101(as earlier described in connection with any one of the embodiments)disposed therein. A plurality of slots s are provided at one side of thewaveguide 4. These slots s are excited in-phase, and radiate waves atmaximum in a cross direction of the waveguide 4. Since thethree-dimensional periodic structure 101 is provided, signalstransmitted through the waveguide 4 are attenuated in unwanted frequencybands, resulting in antenna characteristics with less spuriouseffects/characteristics.

What is claimed is:
 1. A three-dimensional periodic structure,comprising; a first substance having a first dielectric constant, thefirst substance occupying a three-dimensional space and having a secondsubstance having a second dielectric constant which is different fromthe first dielectric constant periodically distributed inthree-dimensional axial directions in the interior of thethree-dimensional space, and (a) a conductor on an external surface ofthe three-dimensional space, or (b) a third substance which is differentfrom the first and second substances embedded in the three-dimensionalspace, or (c) both (a) and (b).
 2. A three-dimensional periodicstructure according to claim 1, wherein the conductor is present and isin the form of a conductive film.
 3. A three-dimensional periodicstructure according to claim 2, wherein space of predetermineddimensions and filled with one of the two substances is present in thethree-dimensional space.
 4. A three-dimensional periodic structureaccording to claim 2, wherein the second substance is air and is arrayedso as to form three-dimensional diamond shaped structures within thethree-dimensional space.
 5. A three-dimensional periodic structureaccording to claim 2, wherein the first substance is a dielectric.
 6. Athree-dimensional periodic structure according to claim 2, wherein thethree-dimensional space includes a void space.
 7. A three-dimensionalperiodic structure according to claim 6, wherein the void space containsa dielectric.
 8. A three-dimensional periodic structure according toclaim 6, wherein the void space contains a ferrite.
 9. Athree-dimensional periodic structure according to claim 6, wherein thevoid space extends inwardly from a peripheral surface of thethree-dimensional space.
 10. A three-dimensional periodic structureaccording to claim 1, wherein the third substance is present.
 11. Athree-dimensional periodic structure according to claim 10, wherein thesecond substance is an air and is disposed as a plurality of holesarrayed in the first substance so as to form a three-dimensional diamondshaped crystal lattice structure, and wherein the third substance isdisposed in a plurality of the air holes.
 12. A three-dimensionalperiodic structure according to claim 10, wherein the three-dimensionalperiodic structure has changed periods along predeterminedthree-dimensional axial directions.
 13. A three-dimensional periodicstructure according to claim 10 disposed on at least one surface of asubstrate which constitutes a part of a transmission path.
 14. Athree-dimensional periodic structure according to claim 13, wherein thesubstrate comprises a transmission line comprising a conductive film.15. A three-dimensional periodic structure according to claim 14,wherein the substrate has a multilayer structure comprising at least onecircuit element.
 16. A three-dimensional periodic structure according toclaim 1, wherein the three-dimensional periodic structure is incombination with a coupling part that is coupled to an electromagneticfield in a resonance mode in the space surrounded by the conductor ofthe three-dimensional periodic structure, thereby creating a resonator.17. A three-dimensional periodic structure according to claim 1, whereinthe three-dimensional periodic structure is in combination with acoupling part that is coupled to an electromagnetic field in atransmission mode in the space surrounded by the conductor of thethree-dimensional periodic structure, thereby creating a transmissionpath.
 18. A three-dimensional periodic structure according to claim 17,wherein the three-dimensional periodic structure includes windows in theconductor of the three-dimensional periodic structure through whichelectromagnetic waves penetrate, whereby an antenna is created.
 19. Athree-dimensional periodic structure according to claim 18, wherein thethree-dimensional periodic structure has different crystal periods inpredetermined three-dimensional directions, and the windows are providedin the predetermined three-dimensional directions with the differentcrystal periods.
 20. A three-dimensional periodic structure according toclaim 18, and a transmission path provided at the window of the antenna,thereby forming a branching filter.
 21. A three-dimensional periodicstructure according to claim 1, disposed as a signal transmission pathof an isolator or a coupler.
 22. A high frequency apparatus containingat least one element selected from the group consisting of resonator,transmission path, antenna, branching filter, isolator, and coupler, inwhich said element comprises a three-dimensional periodic structureaccording to claim
 1. 23. A method of producing a three-dimensionalperiodic structure according to claim 10 by stereolithography,comprising: layer-by-layer, irradiating light onto a light-hardenableresin in individual layers in cross-sectional pattern to be present inthat layer to form the three-dimensional periodic structure, andproviding the third substance during the stereolithography.
 24. A methodof producing a three-dimensional periodic structure according to claim 2by stereolithography, comprising: layer-by-layer, irradiating light ontoa light-hardenable resin in individual layers in cross-sectional patternto be present in that layer to form a three-dimensional periodicstructure, and forming the conductive film by electroless plating.